The present invention relates to a circuit arrangement having a protective function, containing at least two power contactors which have main make contact elements arranged in enable circuits, in each case one main make contact element of a power contactor being connected in series to a main make contact element of another power contactor in the respective enable circuit.
In circuit arrangements having protective functions, goals include, on one hand, to recognize individual faults by carrying out the protective function but, on the other hand, to prevent unexpected starting as well. Protection against unauthorized, unintentional or erroneous closing of dangerous electric circuits should also be ensured. A circuit arrangement having a protective function which, however, contains positively driven relays, is described in German Patent Document No. DE 39 37122 C2. There, a so-called xe2x80x9cfail-safe circuitxe2x80x9d is implemented by a fail-safe AND gate which connects through to the coils of the positively driven relays only if the required safe condition exists, that is if none of the components is defective. In the case of power contactors, a positive drive of main and auxiliary contacts is not possible for design reasons.
Therefore, an object of the present invention is to provide a circuit arrangement having a protective function which fulfills the above-mentioned criteria and which is suitable, in particular, for power contactors.
The present invention provides a protective circuit arrangement. The protective circuit arrangement includes: a first power contactor, the first power contactor including a first coil and a first main make contact element; a second power contactor, the second power contactor including a second coil and a second main make contact element, the second main make contact element being connected in series with the first main make contact element in an enable circuit; a first coil circuit make contact element connected in a first coil circuit of the first coil; a second coil circuit make contact element connected in a second coil circuit of the second coil, the first and second coil circuit make contact elements being capable of being jointly actuated; a first auxiliary contact unit including a first make contact element and a first break contact element, the first make and break contact elements being positively driven; a second auxiliary contact unit including a second make contact element and a second break contact element, the second make and break contact elements being positively driven; a third auxiliary contact unit including a third make contact element and a third break contact element, the third make and break contact elements being positively driven; and a fourth auxiliary contact unit including a fourth make contact element and a fourth break contact element, the fourth make and break contact elements being positively driven. The first, second, third and fourth make contact elements are connected in series in a first indicator circuit; the first, second, third and fourth break contact elements are connected in series in a second indicator circuit; the first main make contact element is disposed between the first and third auxiliary contact units; the second main make contact element is disposed between the second and fourth auxiliary contact units; the first main make contact element and the first and third make and break contact elements are disposed on a common first contact bridge; and the second main make contact element and the second and fourth make and break contact elements are disposed on a common second contact bridge.
According to the present invention, in each case one make contact element is provided in the coil circuit of each coil of each power contactor, the make contact elements being able to be actuated jointly. The main make contact elements of each power contactor are arranged between two auxiliary contact units which each have a make contact element and a break contact element which are designed as positively driven contacts, the make contact elements of all auxiliary contact units being connected in series in a first indicator circuit and the break contact elements of all auxiliary contact units being connected in series in a second indicator circuit. The contact elements of the power contactors and allocated auxiliary contact units are fixed on a common contact bridge.